/*******************************************************************************
 * Copyright (c) 2010-2011 Luaj.org. All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 ******************************************************************************/
package org.luaj.vm2;

/**
 * Subclass of {@link Varargs} that represents a lua tail call
 * in a Java library function execution environment.
 * <p>
 * Since Java doesn't have direct support for tail calls,
 * any lua function whose {@link Prototype} contains the
 * {@link Lua#OP_TAILCALL} bytecode needs a mechanism
 * for tail calls when converting lua-bytecode to java-bytecode.
 * <p>
 * The tail call holds the next function and arguments,
 * and the client a call to {@link #eval()} executes the function
 * repeatedly until the tail calls are completed.
 * <p>
 * Normally, users of luaj need not concern themselves with the
 * details of this mechanism, as it is built into the core
 * execution framework.
 *
 * @see Prototype
 * @see LuaJC
 */
class TailcallVarargs extends Varargs {

    LuaValue func;
    Varargs args;
    Varargs result;

    TailcallVarargs(LuaValue f, Varargs args) {
        this.func = f;
        this.args = args;
    }

//	public TailcallVarargs(LuaValue object, LuaValue methodname, Varargs args) {
//		this.func = object.get(methodname);
//		this.args = LuaValue.varargsOf(object, args);
//	}remove by yanqiu

    public boolean isTailcall() {
        return true;
    }

    public Varargs eval() {
        while (result == null) {
            Varargs r = func.onInvoke(args);
            if (r.isTailcall()) {
                TailcallVarargs t = (TailcallVarargs) r;
                func = t.func;
                args = t.args;
            } else {
                result = r;
                func = null;
                args = null;
            }
        }
        return result;
    }

    public LuaValue arg(int i) {
        if (result == null)
            eval();
        return result.arg(i);
    }

    public LuaValue arg1() {
        if (result == null)
            eval();
        return result.arg1();
    }

    public int narg() {
        if (result == null)
            eval();
        return result.narg();
    }

    public Varargs subargs(int start) {
        if (result == null)
            eval();
        return result.subargs(start);
    }
}